This invention is directed to an improvement in cyanoethylation and other cyanoalkylation processes. The process involved is preferably continuous, although it may also be performed in batch operations. The invention will be further described with reference to cyanoethylation processes, but it is understood that the invention is also useful in connection with other cyanoalkylation processes as further disclosed herein. The improvement of the invention involves limiting the conversion of the cyanoalkylating agent in order to avoid the formation of unwanted byproducts and improve the selectivity for the desired products.
Cyanoethylation refers to the reaction between acrylonitrile and a variety of compounds to yield .beta.-substituted propionitrile derivatives. The compounds are characterized by their possession of a labile hydrogen atom. The latter is a hydrogen atom bonded to an electronegative atom or to an atom activated by strongly electronegative substituents. Classes of compounds containing labile hydrogen atoms include those having hydroxyl groups, e.g., polyhydric alcohols. Cyanoethylation can be generalized by the following reaction formula: EQU CH.sub.2 .dbd.CHCN+RH.revreaction.RCH.sub.2 CH.sub.2 CN
For polyhydric alcohols the general reaction formulas are as follows: EQU CH.sub.2 .dbd.CHCN+HOROH.revreaction.CNCH.sub.2 CH.sub.2 OROH EQU CH.sub.2 .dbd.CHCN+CNCH.sub.2 CH.sub.2 OROH.revreaction.CNCH.sub.2 CH.sub.2 OROCH.sub.2 CH.sub.2 CN
Cyanoethylation products are useful intermediates for the manufacture of plastics and fibers.
Cyanoethylation is used in the formation of a great variety of polyfunctional nitriles, for example, see Encyclopedia of Chemical Technology, Kirk-Othmer, 2nd Edition, Volume 6, and Organic Reactions, R. Adams et al, Volume 5, John Wiley and Sons, New York 1949. Cyanoethylation using ion exchange resin catalyst is disclosed in J. of Org. Chem., Vol. 27, May 1962, pages 1920-1921, "Catalysis by Ion Exchange Resins. Improved Cyanoethylation and Carbamylethylation of Diols".
The cyanoethylation reaction has a tendency to be accompanied by polymerization of the acrylonitrile. It is desirable to avoid the polymerization side reaction since valuable starting material is converted to less valuable byproducts. Techniques suggested to minimize the unwanted polymerization include maintaining a lower temperature by cooling the exothermic reaction, diluting the reaction mixture with an inert solvent, use of soluble or highly dispersed catalyst and the gradual addition of acrylonitrile with mechanical mixing. However, the aforementioned solutions suffered from various shortcomings such as additional capital expenditures, and/or additional materials handling costs, and/or additional separation steps and costs.
In U.S. Pat. No. 2,853,510, a soluble catalyst, a large excess of glycol over acrylonitrile, and gradual addition of acrylonitrile over 8 hours are employed in cyanoethylation of diethylene glycol (Example 4) to obtain 100% conversion of acrylonitrile to cyanoethylethers. Other ways of avoiding undesired byproducts are not suggested. Nor it is suggested that it would ever be desirable to operate at less than 100% conversion of acrylonitrile.
In U.S. Pat. No. 3,324,164, a soluble catalyst and intense mixing are employed in cyanoethylation of methanol (Embodiment I) with stoichiometric proportions of acrylonitrile and methanol, to obtain .beta.-cyanoethyl methyl ether in 99% purity and amount equivalent to a yield of 98% of theory. Again other ways of avoiding undesired byproducts are not suggested, nor is it suggested that it would ever be desirable to operate at less than nearly complete conversion of acrylonitrile.
In U.S. Pat. No. 3,701,802, cyanoethylation of methyl-12-hydroxystearate for example is carried out in batch operation using excess acrylonitrile as solvent for the reaction. In obtaining cyanoethylation to the degree of 76.7% (Table II), relatively very large amounts of acrylonitrile polymer are formed, i.e., 0.4 gram of polymer per 0.5 gram of methyl-12-hydroxystearate. This indicates a total conversion of acrylonitrile well in excess of the stoichiometric amount for reaction with all the methyl-12-hydroxystearate. No practical way is suggested for overcoming the problem of excessive formation of unwanted product while still obtaining a satisfactory degree of cyanoethylation.
Other cyanoalkylation processes are disclosed in U.S. Pat. Nos. 2,280,790; 2,404,164; 2,579,580; 2,836,613; 2,853,510; 3,024,267; 3,150,142; 3,151,150 and 3,957,848. Various degrees of conversion of the compound which is cyanoalkylated are disclosed, but such conversion is distinct from the degree of total conversion of the cyanoalkylating agent, which may undergo polymerization as well as cyanoalkylation reactions. These references do not suggest the importance of limiting the total conversion of the cyanoalkylating agent.
The process of the invention overcomes the aforementioned problem of an unwanted side reaction and avoids the shortcomings of the aforementioned solutions to the problem. By limiting the total conversion of cyanoalkylating agent, as set forth hereinafter, the process of the invention permits obtaining high selectivity for the desired cyanoethylation product, for example 3,3'-ethylene dioxybis(propionitrile) from the reaction between ethylene glycol and acrylonitrile, while the amount of acrylonitrile polymer formed is minimized. Further when certain reactants are used, as disclosed hereinafter, a product intermediate can be recycled and serves as a solvent and facilitates the reaction. Still further the resulting cyanoethylated product stream is of high purity which simplifies subsequent processing.